In the Parallel Universes where Superman exists, Kryptonians don’t appear to have limb regenerative abilities. Even under the yellow sun of Earth that grants them their super powers. Kryptonians will heal near instantly here if nothing is impeding the process. Namely green, or blue Kryptonite. Exposure to said Kryptonite would be the most likely method by which someone could cut off an arm, or leg. If a supervillain were to accomplish this then it would leave Clark Kent, aka Kal-El, with a rapidly healed stump! However plausibly he could grab the severed limb, and place it back into position before healing sets in. Then once the healing starts the limb would theoretically reattach!
Thankfully Jor-El, aka Kal-El’s biological Father, would not stand for his son to endure a handicap. At least not permanently. Temporarily if he wanted Superman to experience such a hardship. More precisely the artificial intelligence meant to replicate the spirit of Jor-El. This AI Jor-El is of course located in the infamous Fortress Of Solitude near the North Pole. Interestingly enough Superman’s Fortress is not too far from Santa Claus’s North Pole City on the parallel Earth’s he exists in. The Fortress Of Solitude offers a multitude of advanced Kryptonian technologies that would allow for limb regeneration. This includes stem cell activation. It’s probably also possible for a human limb to be attached, and then Kryptonian powers would be imbued upon it. Just as we’ve seen humans in the various incarnations of the Superman franchise have powers transferred from Kal-El, or granted by AI Jor-El at the Fortress. Even if all of that wasn’t possible, Superman knows a lot of people with access to a number of advanced experimental technologies such as Bruce Wayne, aka Batman. No doubt Wayne Enterprises, or some other corporation with access to cyborg technology, could give Superman an extremely powerful bionic limb!